This invention relates generally to luminaires and more particularly to a new and improved luminaire having an novel lens structure as described hereinafter.
It is known in the art to provide luminaires having internal reflectors and external lens structures attached to a fixture base for the purpose of directing light in a predetermined manner. Such a luminaire is shown in the Applicant's before-referenced U.S. Pat. No. 4,285,034, issued on Aug. 18, 1981 and invented by Daryl Dean Sullivan. Such prior art fixture utilizes a downwardly positioned fixture base formed around an essentially horizontal round quadrant lens and contains provisions on the internal portion of the fixture base for controlling light as desired and as more fully described in the patent. The Applicant's present invention is designed to result in a predetermined light distribution pattern which is especially useful when uniformity of illumination is desirable and sought by the purchaser of the luminaire.
One of the criteria of a good lighting installation is the uniformity of the illumination. That is, the amount of light per square unit of area should essentially remain constant throughout the area being lighted. The unit that conveys this density or the amount of light per unit area is referred to as a footcandle (fc) or as one lumen of light per square foot of the area.
In the present practice of designing lighting for indoor or outdoor areas, it is desirable to use luminaires, sometimes referred to as lighting fixtures, to provide systematic light distribution patterns. The area being lighted by prior art luminaries contains circular patches of the uniformly distributed light, that is, light of constant footcandles. These circular patches of light are bases of cones of light with apexes at the luminaires. The consequence of using these prior art type luminaires is that the criterion of uniformity of the illumination is really not met as will be more fully described hereinafter. It is not desirable to have the lack of light in the center of the layout that occurs when the patches of light are tangential to each other. It is more desirable if horizontal distances between the luminaires are decreased to add light at the center of the layout but then an excess of light will occur along the sides of the layout. Non-uniformity will still exist in spite of the additional luminaires that are needed to pull the circles of light together in a lighting layout.